Cleaning and regenerating compound for electronic tubes



Aug. 29, 1933. H. J. MILLER 1,925,076

CLEANING AND REGENERATING COMPOUND FOR ELECTRONIC TUBES Filed Aug. 4,1930 far/922$?" 1%rzry IA/22: 7"

Fatentedi Aug. 29,:

CLEANING REGENERATING COM-'- POUNIJFOR ELECTRONIC TUBES Henry JohannesMiller, Chicago, 111. Application August 4, 1930. Serial No. 472,888

2- Claims.

My invention relates to a cleaning and regenerating compound forelectronic tubes.

There is considerable evidence tending to show that in the operation ofdevices having electron emissive surfaces, the emissive discharge is duelargely to a thin film of. metallic alkali or alkaline earth metal. Forinstance, when a barium or strontium oxide coating is used it appearsthat there is what has been termed a monatomic film of metallic bariumor strontium on the surface of the cathode which is responsible forithehigh emissivity of such a coating. However, the presence of too large aquantity of the metal upon the oxide destroys the emissive properties ofthe coating.

In the production of vacuum tubes by the well known methods as by theconversion of carbonates to oxides on the cathode, there is sumcientfree metallic'alkali or alkaline earth metal to produce satisfactoryemission. But after the tube has been'used for some time the film ofmetal is gradually dispersed, and at the same time gases are liberatedfrom the tube elements due to heating and the constant vacuum to whichthey are subjected. 1 Y

An object of my invention is to provide means for replenishing themetallic film on cathode surfaces.

A further object is to provide means for cleaning up the gases of a tubewhich are liberated from the elements. i i

A further object is to provide anew regenerating alloy; 7 Y

A further object is to provide a new'regenerat-f ing and cleaning alloy.

Qther objects-and advantages will appear as the description proceeds.

, Referring to the drawing:

The singleflgure is an elevational View of an ordinary'vacuum tubehaving a-base 5, and an envelope 6 mounted thereon. I

Within the envelope is a stem '7 carrying a plurality of, supports 8upon which elements 9 are mounted. The invention is applicable to avariety of tubes such as vacuum tubes,,gas glow discharge tubes,photo-electric ,cells, etc. The particular type of tube illustrated is aradio audion having an oxide coated cathode such as is well known inthe-art. The. emitting surface upon the cathode is formed by convertinga carbonate to an oxide by the application of heat liberating carbondioxide, which is exhausted from the tube by means of a vacuum pump. The

heating of the elements also causes occluded gases to be expelled fromthe envelope. It apthe elements remain comparatively cool.

vided for removing the excess of the metal from pears that in theformation of the oxide coating, where the coating is formed byconverting a v carbonate of an alkaline earth metal to an oxide of themetal, a thin adsorbed film'of the'metal remains on'the surface of theoxide, and this film acts as the emitting agent. 'After the tube hasbeen in use for some time, the film becomes dispersed and the efliciencyof the tube is lowered. Another factor contributing to the deteriorationof the tube is the liberation of gases from the elements under theheating and vacuum of the tube while in use. I have found that byproviding a pellet of a barium magnesium tin alloy within the tube theemissive surface may be reactivated, and the gases cleaned up in thetube. Thispelletpreferably consists of an alloy con- 1 taining 4.29percent of barium, 7.36 percent of magnesium, and 88.35 percent of tin,these percentages may bevaried to some extent between limits of barium13-12%, magnesium 620% and tin -91%. Apellet ll of this alloy may besecured within the tube in such a position that the pellet may be heatedinductively, independently of the elements. Thus, when the tube is beingexhausted the elements are inductively heated While the pellet remainscomparatively cool, and when the pellet is inductively heated, I haveshown the pellet secured to one end of the electrode supports 8 in aposition Where it may be heated independently of the elements. In ordertoregene rate the tube, the pellet is inductively heated, liberatingbarium and 'magnesium. A portion of the barium is deposited on theoxidecoating of the cathode, and the magnesium acts as a getter to scavengethe gases within the envelope.

It "will, of course, be understood, that other getter materials may beused in the alloy, or that the alloy may be used without a getter. Thetin, which forms the base or main constituent of the alloy, liberatesthe barium or alkaline V earth metal, and the, getter in the requiredminute quantity. 7

In cases Where an alkaline earth metal is liberated from one of itssalts by reaction with another compound upon the application of heat,the amount of alkaline earth metal liberated is invariably too large,and means must be prothe tube.

Thefinvention provides a convenient method 7 of regenerating tubes,'andmay obviously be employed to liberate a quantity of. alkaline earthmetal to form the original deposit upon a cath ode, asin the practice ofmanufacturing photoelectric cells.

What I claim is newand desire to protect by Letters Patent of the UnitedStates is: 1. A vacuum tube comprising an exhausted envelope, electrodesincluding a cathode having a coating of alkaline earth oxide, a pelletin said tube consisting of an 'alloy of tin, barium' and magnesium forscavenging and rejuvenating the tube.

HENRY JOHANNES MILLER.

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